The present invention relates to a method for monitoring and estimating the lighting conditions in front of a moving object in particular in front of a motor vehicle,
In German Published Patent Application No. 195 23 262, a sensor system and an evaluation system are provided to automatically switch lighting units in vehicles. The sensor system has at least one non-directional global sensor that captures the general lighting conditions around the vehicle and at least one directional sensor that captures the lighting conditions in front of the vehicle in the direction of vehicle travel. Based on the signals from the global sensor, the evaluation system can detect a change in the general lighting conditions around the vehicle, for example in twilight, and can turn the lighting units on or off. Based on the signals from the directional sensor, the evaluation system can detect a tunnel or underpass located in front of the vehicle in the direction of vehicle travel and turn the lighting units on in good time before entering the tunnel or underpass.
The disadvantage of this arrangement is the fact that the separate ambient and directional sensors tend to make the system more complex. Photocells to which the incident light is supplied with the help of optical concentrators are used as the light-sensitive elements. This makes the arrangement dependent on shutters and exposure times.
A method in which a vehicle is provided with a side-mounted optical scanning system to provide non-contact scanning of the side road area is described in European No. 0736 414. An evaluation unit is connected downstream from the scanning system. The optical scanning unit includes multiple infrared transmitting elements, arranged side-by-side, and a corresponding CCD array for scanning the road surface to detect the edge of a traffic lane. The evaluation unit is configured to determine runtime and contrast and to detect contours based on the data supplied by the scanning system.
A significant disadvantage that arises when using CCD sensors or even linear CMOS sensors to measure brightness is the fact that they can capture only a limited range of brightness dynamics. As a result, they are provided with electronic or mechanical exposure time controllers and shutters. This makes it impossible to use the signal measured at the sensor output for absolute brightness measurement because the exposure time and shutter position, respectively, should always be taken into account.
The object of the present invention is to considerably simplify the determination of lighting conditions in front of a moving object, in particular in front of a vehicle, so that suitable measures can be taken for the manual or automatic operation of the lights in front of the moving object according to the situation.
The method according to the present invention has an advantage in that it can considerably reduce the mechanical and electrical complexity in determining lighting conditions in the direction of movement in front of a moving object such as, in particular, a vehicle. This is generally achieved with a considerable reduction in the cost of the overall system. The sectoral brightness measurement that this affords vastly increases flexibility.
In the method according to the present invention for determining the lighting conditions in front of a moving object, in particular in front of a vehicle, the brightness measurement is, in principle, carried out with a two-dimensional image sensor, and one or more information values relating to the lighting conditions is generated with the help of a sectoral and/or global evaluation of the brightness values measured by the image sensor in the respective sectors used.
In one particularly advantageous embodiment of the method according to the present invention, a CMOS image sensor is used as the image sensor for the two-dimensional brightness measurement. It is suitable to use an image sensor with a non-linear conversion characteristic to make the best possible use of the existing, frequently quite narrow, current and voltage ranges involved in the high dynamics of light incidence.
In a further particularly advantageous embodiment of the method according to the present invention, a logarithmic image sensor is used for measuring brightness.
In a further suitable embodiment of the method according to the present invention, the brightness is measured by averaging pixel brightness in measurement windows.
In a further particularly suitable embodiment of the present invention, the brightness measurement is combined with an automatic traffic lane tracking system to selectively measure ambient brightness in the path of the traffic lane.
A further advantageous embodiment provides an arrangement for detecting objects, making it possible to eliminate, for example, large trucks traveling a short distance in front of the vehicle in the sectoral brightness measurement.
The arrangement for carrying out the method according to the present invention principally includes a two-dimensional image sensor, onto which the area in front of the vehicle can be or is mapped. A CMOS image sensor, which, in a particularly suitable embodiment, can be a logarithmic image sensor, is advantageously provided as the two-dimensional image sensor. In another embodiment, an image sensor that generally has an advantageous, non-linear conversion characteristic can also be provided.
The method according to the present invention or the arrangement according to the present invention is preferably used, in particular, to give the driver of a vehicle advance warning and alert him to the need to turn on the vehicle lights; alternatively, the method and/or the arrangement is used to automatically activate the vehicle lights in advance, in particular to turn them on and possibly also off again. This makes it possible to respond to tunnel entrances and exits as well as underpasses according to the situation.
The method according to the present invention or the arrangement according to the present invention is also preferably used, in particular, to alert the driver of a vehicle to the need to turn the vehicle lights on and off based on the ambient brightness measured by the two-dimensional image sensor; alternatively, the method and/or the arrangement is used to automatically activate the vehicle lights, in particular to turn them on and possibly also off again, also based on the ambient brightness measured by the two-dimensional image sensor. This makes it possible to respond to global brightness variations caused by daylight, nightfall, cloud cover, twilight, etc.